using System;
using System.Linq;
using NUnit.Framework;

namespace Solver
{
	/// <summary>
	/// Find the greatest product of five consecutive digits in the 1000-digit number.
	/// </summary>
	public class Problem008 : SelfChecker, IProblem
	{
		private static readonly string BigNumber = @"
73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450";

		public int Id
		{
			get { return 8; }
		}

		public string Solve()
		{
			return SolveInternal().ToString();
		}

		private static int SolveInternal()
		{
			var parts = BigNumber.Replace(Environment.NewLine, string.Empty).Split('0').Where(p => p.Length >= 5);
			int maxProduct = 0;
			foreach (var part in parts)
			{
				var digits = part.ToCharArray().Select(c => c - '0').ToArray();
				var product = 1;
				for(int i = 0; i < digits.Length; i++)
				{
					product *= digits[i];
					if (i >= 5) product /= digits[i - 5];
					if (product > maxProduct) maxProduct = product;
				}
			}
			return maxProduct;
		}

		[Test]
		public override void Check()
		{
			Assert.AreEqual(1000, BigNumber.Replace(Environment.NewLine, string.Empty).Length);
			Assert.AreEqual(40824, SolveInternal());
		}
	}
}